I'm curious to hear other's thoughts on they think would be useful.
Please don't hold back ideas! There's very little harm positing silly or unlikely ideas, but there is some potential value (perhaps more than you realize).
Inspired in part by calebo's comment here
This fiscal sponsor org would get to learn a lot about what different EA aligned donors do and don't like donating to, so you could imagine it providing a helpful service to donors (and EA orgs) of suggesting them orgs that they may be interested in checking out, based on their donation patterns. I could imagine this being appreciated by the donors given that it could have enough data points to make genuinely useful recommendations when those opportunities arise.